Method of joining pipes
This application is a continuation, of application Ser. No. 07/195,118, filed May 17, 1988, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a method of joining piping materials, which is suitable for joining two thin-walled stainless steel pipes and for joining a metallic pipe and a metallic pipe coupling. 
     It is well known to join piping materials such as metallic pipes, pipe couplings, etc. with a technique to thread end portions of the piping materials and screw one piping material into the other. However, such method has not been satisfactory with respect to workability, pressure resistance, airtightness, etc. The present applicant has previously invented a joining method to form a diametrically enlarged portion at an end portion of one piping material, i.e. a tapered portion, to which an annular gasket having a wedge-shaped cross-section is interposed and further an end portion of the other piping material is inserted, followed by application of pressure from the periphery to achieve plastic deformation of the diametrally enlarged portion. This is disclosed in Japanese Provisional Patent Publication No. 130729/1982. Also, according to subsequent studies by the present applicant, it has been found that more effective joining can be done by inserting a C ring as shown in Japanese Unexamined Utility Model Publication No. 75582/1986 together with the annular gasket into the diametrally enlarged portion. 
     In the method as mentioned above, for plastic deformation of the diametrally enlarged portion, joining the piping materials to each other was effected by approaching in the axis direction a first jaw having a lateral cross-sectional shape with the tapered planes of clamping action and a second jaw having a tapered planes of clamping action in the opposite direction thereto. Therefore, the jaws of the joining tool are required to move complicatedly, thus causing the size of the joining tool to be too large. This is particularly problematic because it is impossible to effect joining of piping materials near walls. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the problems as described above and to provide an improved method of joining piping materials. 
     The method of joining piping materials according to this invention is characterized by, forming at an end portion of one piping material to be joined a socket comprising a tapered portion which is diametrically enlarged gradually toward the pipe end and a maximum diameter portion extending from said tapered portion with the maximum diameter thereof. Then, an intermediary inserting is fitting along the internal peripheral surface of said tapered portion in the socket to be in intimate contact therewith and thereafter inserting an end portion of the other piping material thereto. The external periphery of said socket is compressed with two clamping members having a lateral cross-sectional shape with the center position as the deepest portion and tapered planes of clamping action on both sides thereof in the radial direction, thereby effecting plastic deformation of said maximum diameter portion in the diameter shrinking direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to 3 are sectional views of the steps for illustration of an example of the joining method of the present invention, respectively. 
     FIGS. 4 to 6 are side views showing an example of the joining tool of the present invention, respectively. 
     FIGS. 7 to 9 are sectional views of the steps for illustration of another example of the joining method according to the present invention, respectively. 
     FIG. 10 is a plan view showing a C ring. 
     FIG. 11 is a sectional view showing the state in which the C ring is impressed against the external peripheral surface at the end portion of the piping material. 
     FIG. 12 is a sectional view of the steps for illustration of still another example of the joining method according to the present invention. 
     FIG. 13 is a side view partially cut away showing another example of the joining tool of the present invention. 
     FIG. 14 is a perspective view partially cut away of the pertinent portion of the joining tool shown in FIG. 13. 
     FIG. 15 is a side view partially cut away showing an enlargement of the pertinent portion of the joining tool shown in FIG. 13. 
     FIG. 16 is a sectional view showing the piping materials before joining. 
     FIG. 17 is a front view partially cut away showing the piping materials joined. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Example 1 
     First, as shown in FIG. 1, at the end portion of one of the two piping materials 1 and 2 which are to be joined, is a socket composed of a diametrally enlarged portion 3 having a diameter slightly enlarged such that the other piping material 2 may be inserted thereinto, a tapered portion 4 being gradually enlarged diametrically from this diametrically enlarged portion 3 toward the pipe end, and a maximum diameter portion 5 extending from said tapered portion 4 parallel with the pipe axis. This tapered portion 4 is preferably allowed to form an angle θ 1  of about 10° to 30° with the center axis of the piping material 1 in a cross-section cut along the plane including the axis of said piping material 1. 
     Next, after an annular gasket 7, which comprises synthetic material such as an ethylene propylene rubber (EPDM), having a wedge-shaped cross-section to be disposed in intimate contact with the internal peripheral surfaces of the tapered portion 4 and the large diameter portion 5 are inserted into the socket, and then the end portion 6 of the other piping material 2 is inserted thereinto. 
     As shown in FIG. 2, the external periphery of the above socket is sandwiched between a joining tool 11 provided with two clamping members 10, 10 each having a wedge-shaped cross-section with the center position as the deepest portion and tapered planes of clamping action 8, 9 formed on both sides thereof. 
     The joining tool 11, as shown in FIGS. 4 to 6, is provided with two clamping members 10, 10 each having the above tapered planes of clamping action 8, 9 at the tip end side and an actuating lever 12 at the base end, a pair of front and back connecting plates 14, 14 supporting mutually these clamping members 10, 10 with the above tapered planes of clamping action 8, 9 opposed to each other, clamping members 10, 10 are freely rotatable around rotational axes formed by pins 13, 13. A spring member, for example, a plate spring 15, is fixed at a predetermined position on the tapered planes of clamping action side of one clamping member 10, elastically supports the other clamping member 10 and urges the tip ends of the both clamping members toward the closing direction. 
     Clamping members 10, 10 are made to have their tip ends separate by pressing actuating levers 12, 12 of both clamping members 10, 10 toward each other with the hands by a user when the joining tool is used. When the pushing rod 16 having a curved surface on the tip end is pushed between the actuating levers 12, 12 of both clamping members 10, 10 by hydraulic pressure, etc., as shown in FIG. 5, FIG. 6, the tip end of the pushing rod 16 is guided by the guide faces 12a, 12a which are formed on the base end of each actuating lever 12 and have curved shapes, whereby the base end sides of the both clamping members 10, 10 are pushed to open and the tip ends of the clamping members 10, 10 are closed with a strong force based on the principle of leverage with the pins 13, 13 as the supporting points. 
     In this case, the spring member may of any type, provided that it can urge the tip ends of both clamping members 10, 10 during non-use toward the closing direction, and other than the above plate spring 15, coil springs provided at the base end sides of both clamping members 10, 10 for urging both members 10, 10 toward the closing direction may be also employed. 
     With the clamping members 10, 10 of such joining tool being mounted, as shown in FIG. 2, at the external periphery of the socket so that one of the tapered planes of clamping action 8, 8 may contact the tapered portion 4 of the piping material 1, the pushing rod 16 of the joining tool 11 is pushed to close the clamping members 10, 10. As a result, as shown in FIG. 3 the maximum diameter portion 5 immediately adjacent to the tapered portion 4 is compressed in diameter toward the pipe end by the other tapered planes of clamping action 9, 9 of the clamping members 10, 10 to be plastically deformed in tapered form. 
     Therefore, the annular gasket 7 is pushed strongly toward the tapered portion 4 side by the plastic deformation of the maximum diameter portion 5. Through the wedge action by the pushing pressure, the annular gasket 7 is compressed between the internal peripheral surface of the socket and the external peripheral surface of the end portion 6 of the other piping material, and is consequently pressed firmly against these surfaces through its restoring force. As a result, good air tightness and pressure resistance are obtained. 
     Example 2 
     The second example shown in FIG. 7 uses as a intermediary insert, in addition to the above annular gasket 7, two C rings 17 which are in close contact with the internal peripheral surface of the maximum diameter portion 5 and the pipe end side face of the annular gasket 7, and the joining tool used is the same as in Example 1. 
     Similarly as in Example 1, the maximum diameter portion 5 continuous to the tapered portion 4 is compressed in diameter as shown in FIGS. 8 and 9 toward the pipe end by the clamping members 10, 10 of the joining tool 11 to effect plastic deformation thereof in tapered form. As a result, the annular gasket 7 is compressed between the internal peripheral surface of the socket and end portion 6 of the other piping material. Simultaneously, the C rings 17, 17 are compressed against the external peripheral surface of the end portion 6 of the other piping material, whereby a better tightness and pressure resistance than in Example 1 can be effected. 
     The C ring 17 may be one punched out in planar C-form from a steel plate as shown in FIG. 10, but may preferably have a sharp rim 17a being provided on the pipe end side along the entire internal peripheral surface of said ring 17 which is to be compressed against the external peripheral surface of the end portion 6 of the other piping material. As shown in FIG. 11 which shows its cross-sectional shape, said C ring 17 has a construction such that the cornered edge 17b formed along the internal peripheral surface of the ring 17 on the annular gasket side may have an acute angle, preferably such that the angle θ 2  formed between the internal peripheral surface of the ring 17 forming this cornered edge 17b and the external peripheral surface of the end portion 6 of the piping material 2 may be about 5° to 15°, more preferably 10°, and that the cornered edge 17c formed along the external peripheral surface of the ring 17 on the pipe end side may also have an acute angle. 
     The reason is because the C ring 17 can be readily compressed against the external peripheral surface of the end portion 6 of the other piping material 2. Thus, 17b, 17c when a strong pull-out force is exerted on the joined two piping materials in the directions as shown by the arrows P, the sharp cornered edges 17c, 17b are compressed, respectively against the internal peripheral surface of the maximum diameter portion and the external peripheral surface of the end portion 6 of the other piping material 2 of the socket, thereby giving rise to a pull-out resistance which resists said pull-out force. 
     Example 3 
     As shown in FIG. 12 an annular gasket 7 having a wedge-shaped cross-section is disposed in intimate contact with the internal peripheral surface of the tapered portion 4, a back-up ring 18 is disposed in intimate contact with the internal peripheral surface of the maximum diameter portion 5 and the pipe end side face of the annular gasket 7. A C ring 17 is disposed in intimate contact with the internal peripheral surface of the maximum diameter portion 5 and the pipe end side face of the back-up ring 18. The joining tool used has the same construction as in Examples 1 and 2. 
     The back-up ring 18 has an external diameter which is closely contacted on the internal peripheral surface of the maximum diameter portion 5, and may be made of any material, provided that it has rigidity capable of preventing insertion of the annular gasket 7 into the gap 17d (see FIG. 10) of the C ring when pressure is applied. 
     According to this Example, through the intermediary presence of the back-up ring 18, during application of pressure, annular gasket 7 will not be pressed into the gap 17d of the C ring 17. Consequently, improvements in air tightness, pressure resistance relative to the other Examples can be effected. 
     Example 4 
     The joining tool shown in this Example is a further improvement of the joining tool shown in the above Examples 1 to 3, but the joining method of piping materials is the same as for the respective Examples described above. 
     This Example is described in detail below by referring to FIGS. 13 through 17. 
     The joining tool 20 has a pair of clamping members 23, 23 mounted freely at both ends of a pair of front and back connecting plates 21, 21 with pins 22, 22 as rotational axes. 
     In the jaw frame 24 at the tip end side of each clamping member 23, half cylindrical clamping jaw 25 is equipped with tapered planes of clamping action 25a, 25b with the center position as the deepest portion. 
     As shown in FIG. 14, on both sides of the jaw frame 24, pipe holders 27, 27 are mounted by bolts 26, and the half cylindrical clamping jaw 25 is supported freely rotatably with respect to the jaw frame 24 by fitting arc-shaped jaw plate portions 25c, 25c provided at the periphery on both ends of the half cylindrical clamping jaw 25 as described above into the arc-shaped grooves 27a at the inside of the pipe holders 27, 27. 
     At the tip end faces of the respective jaw frame 24, 24, flat square holes 28 are provided, and into each hole 28 is inserted plate spring 29. By stopping the tip ends of the respective plate springs 29, 29 as engaged on the engaging cuttings 30, 30 provided on the tip end sides of the clamping jaws 25, 25, the end faces at the tip end sides of the clamping jaws 25, 25 are slightly protruded from the biting faces 24a, 24a of said jaw frames 24, 24. 
     The numeral 31 is a grip lever with two crotch portions 32 formed at the tip end, having the connecting plates 21, 21 as described above mounted at the tip end with an axial pin 33. Actuating levers 23a, 23a which are formed at the base end sides of the clamping members 23, 23 are interposed between said two crotch portions 32 and have guide faces 23b, 23b with curved shapes on the base ends thereof. Said grip lever 31 is provided with a pushing rod 34 having a curved surface at the tip end which is pushed by a hydraulic cylinder (not shown) between the above actuting levers 23a, 23a having guide faces with curved shape, pushes to open said actuating levers 23a, 23a and forces the jaw frames 24, 24 of both clamping members 23 and 23 to engage with each other. The numeral 35 is a plate spring for permitting both clamping members 23, 23 to hold the closed posture during application of no load. 
     The method of joining piping materials by use of the above joining tool is described below. As shown in FIG. 16, with the annular gasket 7 having a wedge-shaped cross-section and the C ring 17 being inserted into the tapered portion 4 formed at the end portion of the piping material 1 and the maximum diameter portion 5 continuous thereto, the end portion 6 of the piping material 2 is inserted. 
     Subsequently, the jaw frames 24, 24 of both clamping members 23, 23 are opened by expansion until the maximum diameter portion 5 of the piping material 1 can be inserted, thereby permitting one tapered planes of clamping action 25a of the half cylindrical clamping jaws 25, 25 fitted in said jaw frames 24, 24 to contact the tapered portion 4 of the piping material 1. Next, the pushing rod 34 is pushed between the actuating levers 23a, 23a formed at the base ends of the clamping members 23, 23 to close the jaw frames 24, 24. Then, the maximum diameter portion 5 continuous to the tapered portion 4 of the piping material 1 is compressed in diameter in the radius direction by the other tapered plane of clamping action 25b of the clamping jaws 25, 25, thereby plastically deforming gasket 7 in tapered form simultaneously with compressing of the C ring 17 against the surface of the piping material 2, to effect joining as shown in FIG. 17. 
     At this time, in the present invention, the clamping jaws 25, 25 are fitted freely rotatably in the jaw frames 24, 24, and also the end faces on the tip end side of said clamping jaws 25, 25 are slightly protruded from the biting faces 24a, 24a of said jaw frames 24, 24 under elastic repulsion of the plate springs 29, 29, whereby the tip end sides of the clamping jaws 25, 25 are narrowed earlier than the biting faces 24a, 24a of the jaw frames 24, 24 during clamping of the jaw frames 24, 24 and there is no inconvenience that the joined portion is extruded to the forward side of the clamping members 23, 23 during clamping. 
     When clamping is further continued, clamping can be done while the tip end faces of the clamping jaws 25, 25 are rotated against the plate springs 29, 29 to the same positions of the biting faces 24a, 24a of the jaw frames 24,24 to effect uniform joining. 
     In this Example, as apparently seen from the above description, the clamping jaws 25, 25 are fitted freely rotatably in the jaw frames 24, 24 of a pair of clamping members 23, 23, and tip end sides of the clamping jaws 25, 25 are slightly protruding from the biting faces 24a, 24a of said jaw frames 24, 24. Here, during joining of the piping materials, since the center of the clamping movement (pins 22, 22) and the center axis of piping materials are eccentric from each other, the clamping members 23, 23 undergo clamping movement while drawing an arc-shaped locus with the pins 22, 22 for rotational axes as the centers similarly as the clamping members 10, 10 in the above respective Examples. For this reason, the clamping members 23, 23 at the end sides near the pins 22, 22 will contact piping materials earlier, whereby the piping materials are pushed forward to the tip end side of the clamping members 23, 23. As a result, it may be considered that correct joining may be sometimes obstructed and pressure resistance at the joined portion slightly lowered similarly as in the above Examples. 
     Whereas, since the tip ends of the clamping jaws 25, 25 are slightly protruded from the biting faces 24a, 24a of the jaw frames 24, 24, the tip end sides of the clamping jaws 25, 25 are closed preceding to the jaw frames 24, 24 and therefore joining can be correctly effected on the center axis of piping materials.